In a vacuum processing apparatus that carries out a vacuum processing, such as etching or chemical vapor deposition (CVD), vacuum cannot be used for holding a substrate on a mounting table. Further, in order to prevent the substrate from being damaged (scratched, bent or the like.) by a mechanical chuck, an electrostatic chuck is generally used.
For example, as shown in FIG. 11, an electrostatic chuck 100 is provided on the surface of the mounting table 102 in a vacuum processing vessel 103 and includes a dielectric material 122 and a sheet of an electrode 121 embedded therein the dielectric material 122. The electrode 121 is connected with a power supply (not shown). By applying a voltage to the electrode 121, the electrostatic chuck 100 is adapted to adsorb the substrate 110 mounted thereon by electrostatic force.
A gas shower head 104 is provided on top of the electrostatic chuck 100. A processing gas supplied from a gas supply line 105 is converted into a plasma between the gas shower head 104 and the mounting table 102 by a high frequency power supplied from the power supply (not shown). As a result, the substrate 110 is etched.
During an etching process, the temperature of the substrate 110 is increased by, e.g., heat applied from the plasma. Hence, by circulating a coolant, e.g., cooling water of a coolant source 107, through a coolant channel 106 provided in the mounting table 102, the substrate 110 can be maintained at a processing temperature, of, e.g., tens of degrees due to the balance between the heat applied from the plasma and heat transferring to the mounting table 102 (cooling by the mounting table 102). Further, since the surface of the electrostatic chuck 100 is uneven on a microscopic scale, cooling gas (so-called backside gas), i.e., temperature control gas, is supplied through a gap between the substrate 110 and the electrostatic chuck 100, so that the heat of the substrate 110 is dissipated toward the electrostatic chuck 100 via the cooling gas.
However, when the electrostatic chuck 100 is repeatedly used, i.e., when the number of processed substrates 100 is increased, the surface of the dielectric material 122 becomes worn by contacting with the substrate 110, thereby becoming smooth, as shown FIG. 12A. As such, the contact area with the substrate 110 increases from S1 to S2. For this reason, the amount of heat transferred from the substrate 110 to the electrostatic chuck 100 through this contact portion is increased, so that the temperature of the substrate 110 is gradually decreased, as shown FIG. 12B. The temperature change may become considerably large, particularly in a process in which the pressure of the cooling gas is low. Since the temperature of the substrate 110 has a some margin with respect to the processed state of the substrate 110, the temperature of the substrate 110 is set to be a specific temperature by controlling the flow rate of the coolant or the like at the side of the mounting table 102 when the electrostatic chuck 100 begins to be used, and then continues to be used without change generally.
However, if the temperature of the substrate 110 is greatly decreased, e.g., about 10° C. to 15° C., a defect may occur on a lot bases, and thus it is necessary to predict the residual life span of the electrostatic chuck 100. Further, since the cooling gas is a part of the heat transfer media between the substrate 110 and the electrostatic chuck 100, the temperature reduction of the substrate 110 can be suppressed by reducing the pressure of the cooling gas. However, if the surface of the electrostatic chuck 100 is worn, the heat transfer rate through the contact portions with the substrate 110 is high. In such a case, therefore, the temperature of the substrate 110 may not be changed a lot by the pressure change of the cooling gas. As a result temperature regulation based on the cooling gas is not effective, and thus is not carried out.
Two types of electrostatic chuck are known, one of which is a Johnson Rahbek type (hereinafter referred as a “JR type”), which adsorbs the substrate by using the electrostatic force generated between the substrate and the surface of the electrostatic chuck, and the other is a Coulombic type, which adsorbs the substrate 110 by using the electrostatic force generated between the substrate and the electrode. In the JR type electrostatic chuck, the electric current flowing through the electrode is high, and adsorptive force is unstable. In contrast, the Coulombic type electrostatic chuck has a low electric current value and stable adsorptive force. Hence, the Coulombic type electrostatic chuck is more frequently used. In the JR type electrostatic chuck, a temporal variation in the electric current value caused by the increase in the contact area is great, so that the electric current value can be used as the index of the life span. On the contrary, in the Coulombic type electrostatic chuck, such a temporal variation in the electric current value is small, and thus the electric current value cannot be used as the index of the residual life span of the electrostatic chuck.
Further, in the actual plasma processing apparatus, a plurality of processing recipes, and setting temperatures for the substrate are prepared. In addition, the margins of the setting temperature are not various. Therefore, the temperature of the substrate cannot be employed as the index of the residual life span.
Japanese Patent Laid-open Application No. 2003-133404 (especially para.0027 and FIG. 8) discloses a technology for predicting the characteristics of the electrostatic chuck prior to the use thereof. However, the index used therein is a current, voltage or the like, so that the residual life span of the electrostatic chuck cannot be predicted while the electrostatic chuck is in use. Thus, the aforementioned problem cannot be solved.